How to use read more tab?

I reader today suggested I break up my blog by using the "read more" tab so that my page doesn't scroll on and on and on. I think its a great idea, so I tried to edit a post, and I see where I can insert the more tab, but then it doesn't do anything to my post. How do I go about using this feature so that after a couple of paragraphs my readers will have to click to read more?

Please be aware that the splitting of content means "the more tag" will only appear when the post in question is on the front page of the blog. When the title is clicked and the post is seen on its own page it will not appear. And when it moves off the front page it will no longer appear.